diff --git a/scripts/serial_command.py b/scripts/serial_command.py
index 46cc290..5bd179a 100644
--- a/scripts/serial_command.py
+++ b/scripts/serial_command.py
@@ -61,10 +61,10 @@ class UBoot:
         self.port.flush()
         output, _ = self.read_prompt(timeout)
         # Query immediately, before another command changes the return status.
-        self.port.write(b"echo __UBOOT_STATUS_${?}__\r")
+        self.port.write(b"echo __UBOOT_STATUS_ $?\r")
         self.port.flush()
         status, _ = self.read_prompt(5)
-        codes = re.findall(r"(?m)^__UBOOT_STATUS_(\d+)__$", status)
+        codes = re.findall(r"(?m)^__UBOOT_STATUS_ (\d+) *$", status)
         if codes != ["0"]:
             raise RuntimeError("Command failed or its exit status could not be verified: " + command)
         if ERROR.search(output):